First Online: 24 July 2010Received: 12 March 2010Accepted: 10 July 2010

Abstract

The transition in a marine boundary layer MBL from stratocumulus topped to shallow cumulus topped is investigated by using a large eddy simulation LES model. The experiments performed aim to examine the influence on the transition of 1 the probability of buoyancy reversal at the MBL top i.e. situations in which the mixture of two air parcels becomes denser than either of the original parcels due to phase change or other nonlinear processes involved in the mixing, and 2 the degree of decoupling in the MBL i.e. the strength of a shallow stably stratified layer near cloud base. Our results suggest that a stratocumulus-topped MBL is most likely to transit to a cumulus-topped one when 1 there exists high probability of buoyancy reversal at the MBL top, and 2 the MBL is decoupled due to large surface evaporation. We argue that a parameterization that includes representation of those two effects combined has the potential to provide a simple way of predicting the MBL transition in climate models.